Thermal environmental and energy effects of vertical greening system under the influence of localized urban climates

Abstract

Vertical greening system (VGS) can cool adjacent urban space and lower building conditioning energy use without consuming valuable land area, however the influence of local microclimate on the effects is understudied. To better understand how VGS behaves environmentally in localized urban climates, the study investigated the outdoor cooling and building energy-saving potential of a VGS in five local climate zones (LCZ) in Shanghai, using integrated modeling with ENVI-met and EnergyPlus. The model verification reasonably reflects the relative differences in thermal effects of VGS due to local climates. The result reveals that, under the maximum inter-LCZ differences in air temperature (Ta) and relative humidity (RH) of 1.4 °C and 5.3 %, the greatest inter-LCZ variations in cooling and humidifying effects of the VGS are 0.16 °C and 1.1 %, respectively. The VGS creates greater adjacent Ta reduction in higher-ranked LCZs, by up to 0.27 °C, but increases RH by 1.6 %. In summer, the VGS provides energy savings of 132–278 Wh/m2 with energy saving rates of 5.7–11.7 %. The annual energy savings are partially offset by the increase in winter heating, and the annual energy saving rates are reduced to 3.2–6.3 %. Of the savings, 92 % is due to shading, 8 % to cooling, and the humidifying effect has a negative impact (- 11 %). The findings underscore the impact of localized urban climates on the VGS thermal and energy performances, and support climate-responsive and performance-optimized urban VGS planning and application.